At present, a typical reagent system used for a method for measuring a body fluid component (e.g., serum, plasma, or urine) is an oxidizing reagent system in the field of clinical chemistry. In such an oxidizing reagent system, an oxidase, which is selected depending on a predetermined analyte such as cholesterol, reacts with an analyte in the presence of oxygen such that hydrogen peroxide is generated. The generated hydrogen peroxide oxidizes a preferable oxidation/reduction indicator in the presence of a substance having peroxidative activity such that color conversion due to oxidization is observed. Then, the color intensity is measured by visual observation or a measurement device. Thus, the analyte concentration in a body fluid sample can be quantitatively measured.
Measurement is influenced by a negative error due to a reduction action of various body fluid components such as a reducing substance, e.g., ascorbic acid, hemoglobin, erythrocyte catalase, or bilirubin. Also, a pigment such as hemoglobin or bilirubin causes a positive or negative error depending on measurement wavelength. In addition, it has been widely known that absorption by such pigment varies with time during measurement due to influence of light, measurement reagent composition components, and the like. This influences measurement results. Such influence is referred to as “interference.”
A variety of methods for reducing interference caused by body fluid components have been studied, regardless of types of measurement methods. For instance, a number of methods, including many methods for reducing interference caused by hemoglobin, have been reported.
JP Patent Publication (Kokai) No. 5-269106 A (1993) discloses a method for reducing interference, which comprises allowing a blood sample to come into contact with an insoluble copper complex containing a high-molecular substance having multiple pendant carboxyl groups and forming an insoluble reaction product with hemoglobin in the blood sample, which can be removed from the blood sample by a solid//liquid separation technique. In addition, JP Patent Publication (Kokai) No. 9-119932 A (1997) describes a finding that temporal changes in the hemoglobin absorption wavelength can be reduced upon optical absorption measurement by setting a measurement wavelength of 517 nm to 529 nm or 580 nm to 592 nm. Based on the finding, the reference discloses a method for reducing such changes in a dry analytical element at a more preferable measurement wavelength of more preferably 520 nm to 526 nm or 583 nm to 589 nm. Further, WO2002/086151 describes that interference caused by hemolyzed hemoglobin can be reduced by addition of at least one or two of thiodiglycol acid, β-thiodiglycol, methionine and the like to a reagent in the measurement of biological components. However, it cannot be said that the above methods sufficiently resolve problems of interference particularly caused by hemolysis observed in a dry analytical element.